I recently shielded my Squier Mustang this week with conductive copper tape. I put it in the pup cavity, control cavity, pick guard, and on top of the control plate. I soldered a wire from the control cavity to the pup cavity, measured with a multimeter and they were in sync with one another. I noticed the bridge ground wire wasn't soldered to the post, so I put a small piece of copper tape on the post and soldered the bridge ground wire. I wasn't sure if that was necessary or would cause problems, but if anyone has input on that I'd appreciate it. I went and plugged it in and it sounded great! No large hums or anything, but today when I plugged in to play I'm getting this crazy buzz, kind of like static?

The thing is that the buzz only comes when a single pickup is on, or when both pickups are out of phase with each other. Certain parts of my room create this buzz, and others are completely silent. The sound is some sort of electro wave (not sure if this is the correct term), sounds like a blaster just buzzing. I'm not sure if I've made a mistake with my shielding, but when I read the multimeter it looked okay. What I'm now wondering is should I solder wires from the bottom of the cavities to the top of the pick guard and the control plate? I made sure to overlap the tape in the cavities when I did the job so they'd touch. The temperature here in the northeast dropped in the past few days, and the air is pretty dry.

The thing is that even before I shielded the guitar, when the pups were out of phase I got this crazy buzz sound too, is this common for these models? This is my first mustang btw. I'd provide pictures but I don't want to take the guitar apart unless I absolutely have to. Any tips are appreciated, I'm not sure exactly what is going on. I've searched around but haven't found any answers yet. thanks!
First thing to do is eliminate house wiring and guitar cables. Take it to a friend's house, see if it does the same thing. And use a different guitar cable. Nothing but guitar, amp and cable, to eliminate noise from effects and make sure no flourescent lights are on.

The ground wire shouldn't absolutely have to be soldered to the bridge, most of mine are just held in place by putting the wire around a screw and making sure that screw is tight. A couple, like tele types, are just held under the bridge plate by the regular screws. If I understand your description right, the way you did it should be ok.

Shielding does not eliminate all types of noise, just electromagetic interference and things like picking up radio stations. It won't do much about hum from faulty house wiring, neon or flourscent lights, bad ground and so forth.
Hmmm...I wonder what this button does...
If it makes that noise when your hand is in contact with the pickguard it could be static from the pickguard itself. Try rubbing the pickguard with Bounce or some other dryer sheet.